Radio impulse system



Sept. 3, 1946.

N. H. YOUNG, JR

RADIO IMPULSE SYSTEM y Filed Dec. 15, 1942 PULSE INPUT 7 [12' 1 ,1 1%H4753 CLIPPER '34 INVENTOR. IVO/PMFIN h. you/v6, JR.

BY my Patented Sept. 3, 1946 UNITED STATES ATENT OFFICE RADIO IMPULSESYSTEM ware Application December 15, 1942, Serial No. 469,044 6 Claims.(Cl. 178-44) This invention relates to radio impulse systems and moreparticularly to systems for selectively filtering pulse modulated wavesin accordance with the amplitude of the pulses.

In the copending application of D. Grieg entitled Receiver system,Serial No. 467,516, filed December 1, 1942, methods and means aredisclosed for selectively filtering a wave modulated with pulsesdiffering in amplitude so as to eliminate unwanted pulses whether or notthey are of less or greater amplitude than wanted pulses.

It is an object of my invention to provide an additional method andmeans for accomplishing the same result.

Another object of my invention is to provide a method and means foramplifying a pulse modulated wave to reduce the amplitude of the pulsesgreater than a given amplitude.

The reduction in amplitude or the elimination of the pulses of amplitudegreater than a given amplitude such as the amplitude of a Wanted pulseis accomplished in accordance with my invention by applying the pulsemodulated wave to an amplifier having an input-output characteristicsuch that an increase of input potential causes the output thereof toincrease to a maximum and then to decrease toward zero. The gain of theamplifier may be adjusted so that the peak of the wanted pulse lies nearthe maximum of the input-output characteristic so that the wanted pulseis amplified a desired value and the pulses of greater amplitude aredistorted. The distortion produces sharp pulse portions defining theleading and trailing edges of the larger pulses according to the amountsthey extend beyond the maximum of the amplifier input-outputcharacteristic. These sharp pulse portions are limited in amplitude bythe maximum of the input-output characteristic of the amplifier. Theamplitude of the sharp portions may be reduced further by passing theoutput of the amplifier through a filter to eliminate the higherharmonics. This reduces the amplitude of the sharper pulse portions withrespect to the amplitude of the wanted pulse which, of course, is ofgreater duration than the duraton of the sharp pulse portions. By properadjustment of the gain of the amplifier and the proper filtering of theoutput thereof, an output will be obtained in which the wanted pulseshave greater amplitude than the unwanted pulses. By clipping this pulseoutput at a level beyond the maximum amplitude of the unwanted pulses, apulse wave will be obtained containing the pulse energy according to theoccurrence of the 2 wanted pulses with substantially a completeelimination of unwanted pulses.

For a further understanding of the invention reference may be had to thefollowing detailed description to be read in connection with theaccompanying drawing, in which:

Fig. l is a schematic illustration of a circuit in accordance with myinvention, and

Fig. 2 is a graphical illustration showing the pulse reduction andeliminating features of the invention.

Referring to Fig. 1, the pulse reducing and eliminating system of myinvention comprises an amplifier circuit ID, a filter l2 and a clipperIS. The amplifier circuit may comprise any arrangement of elementswhereby an input-output characteristic is established so that anincrease of input potential causes the output to increase to maximum andthen to decrease toward zero. Such a. characteristic is illustrated atIS in Fig. 2.

For purposes of illustration, I have shown in Fig. 1 an amplifiercircuit comprising an input vacuum tube l6 having zero bias and twoamplifier tubes 2| and 22 the grids 23 and 24 of which are connected tothe anode I1 and the cathode l8 of the tube IS in push-pull arrangement.The anode I l is provided with a positive bias through a resistor I 9,and is connected to the grid 23 through a coupling condenser 2'5. Thegrid 23 is provided with a negative bias C1 through a resister 21. Thecathode l8 of the tube I6 is connected through a resistor 28 to ground.The cathode I8 is also connected to the grid 24 through a couplingcondenser 29. The grid 24 is biased negatively by a potential C2 througha resistor 30. The cathodes of the tubes 2| and 22 are connectedtogether and grounded at 32. The anodes or plates of the tubes 21 and 22are connected together to provide an outlet 33, the latter beingconnected to a positive potential through a resistor 34.

The input tube l6 operates to apply the input pulse or potential to tube22 without inversion of polarity and simultaneously to apply the inputpotential to tube 2| with inverted polarity. In the absence of an inputpotential, the tube 2| is biased beyond plate cut-oil while the tube 22is biased to a value permitting a normal plate current. As the grid Idof tube 16 is made increasingly negative by an increasing inputpotential, the grid 24 of tube 22 is made more and more negative therebyresulting in a reduction of its plate current. This causes a risingpotential to occur at the plate output connection 33 as indicatedbetween points and 4| on the ever,

are the unwanted pulses.

Fig. 2. At point 4|, tube 22 is at cut-off. During the interval betweenAll and M the Voltage on the grid 23 of tube 2! increases in a positivedirection, but since bias C1 is so chosen to cause the tube 2| to remainat cut-off, the tube contributes nothing to this part of the curve.However, the instant tube 22 reaches cut-off, the grid potential of tube2! begins to rise above cut-off. As the amplitude of the input potentialcontinues to rise, the grid 23 of tube 2| becomes more and more positiveand the tube conducts more and more current causing the potential at theplate connection 33 to decrease as indicatedbetween 4| and 42 on thecurve l5. put potential has reached a value sufficient to cause cut-oilof the tube l6 and any further increase in potential on the grid H! ofthe tube l6 results in no further change in potential at 33.

While I have shown the increasing and decreasing portions ofthecharacteristic curve l5 to have substantially the same slope .in theinverse direction, it will be understood that the characteristics of thetubes may be such as'to provide curve I5 of plate current entirelydifferent slopes anduifie'ent maximum and minimum ipoints M and M1, 42'respectively, for the curve. The main feature of the invention, however,is 'toprov'ide the input. and output characteristic curve with a maximumpoint whereby pulses applied to the amplifier extending in amplitudebeyond the maximum point of the curve are distorted and limited in"amplitude.

Assume that the'input to the grid M of the tube H3 is a modulated wavehaving a series of pulses '5l, 52, '53 and 54,*with the pulse 5| re-'peated as indicated. The wave, of course, may contain other pulseswhich occur at random or ata given frequency not shown with the groupillustrated in Fig. -2. "The pulses illustrated, howare representativein that the pulse 5| is the wanted pulse while the pulses-52, 53 and 54The 'pulses '52 and '53 are of greater amplitude than the 'wanted pulsewhile the pulse 54 is "of less amplitude.

To eliminate the unwanted pulses, the gain of the amplifier H) isadjusted so that'the amplitude of the wanted'pulse 5| is brought nearand preferably slightly under the maximumpoint 4| of the input-outputcharacteristic of the amplifier. The output pulse 51a is therebyproduced in substantially'the same shape as the input pulse "5|. Thepulse52, however, is greatly distorted since it extends beyond 'themaximum point 4| and-in fact beyondthe 'tzero point 42 of the curve.When this pulse is applied to the ampliher, the tube 2| passes the pulsepotential up to the maximum level as indicated at'=a'"thereby producinga leading 'edge'55. Then the tube 22 takes over for the potential of thepulse above the level a thereby providing "a'return trailing edge 55 tozero. The decreasing potential on the trailing sides of the pulse-52provides a second sharp pulse from zero aSJin'dicated by'the leadingedge 51 which extends to'the level a'for the maximumpoint '4 The tube'ZI "then takes over for theremaining decrease in potential below thelevel a thereby providing a'trailing edge 58. Thus, the distorted pulseoutput for the large input pulse 52 provides a sharp pulse 52a whichdefinesithe leadin'g edge of the'input pulse 52 and a second sharp pulse521) which defines the trailing edge "thereof. The "amplitudes of thepulses 52a and 52b are limited by'the maximum point 4| of thecharacteristic curve l5.

The third input pulse At point 42 the in- 53,'while of amplitude greaterthan the pulse 5|, does not extend through the decreasing portionbetween the maximum 4| and the zero point 42 of the characteristic curveI5. The output for the pulse 53 is shown at 53a. The leading edge of thepulse 53 provides a leading edge 60 for the pulse 530. which extends tothe level a. Since the input pulse 53 extends above the maximum level athe tube 22 takes over and provides a decreasing or trailing edge 6|until the top level b of the pulse 53 is reached. This provides a sharppulse portion overlying the leading edge the input pulse 53 decreasesthe potential input applied to theamplifier, a return through thecharacteristic curve is obtained whereby a second sharp pulse portion 54is formed defining the trailing edgeof the output pulse 53a. The pulse53 is thus distorted by the portion thereof extending beyond the maximum4| of the characteristic curve l5.

Thepulse 54 of amplitude less than the wanted pulse 5| providesan outputwhich in accordance with the adjustment of the amplifienmay be smalleras indicated at 55a than the input pulse 54.

As shown in Fig. '2, the pulse portions 52a, 52b,

53 and 54 defining the leading and trailing edges of the larger input"pulses-52 and *53 respectively,

are sharper pulses than the pulse 'output'SIa of the wanted'pulse 5L Bysuitably filtering out the higher harmonics, the sharp pulse porfinaloutput wave 80 is obtained having pulse energy 8| which correspond tothe pulses 5|. Thus, the interfering 'pulses 52, 53 and 54 areeffectively eliminated. The outputpulse energy 8| may, of course, besharpened or otherwise treated as may be desired depending on the useintended forthe pulse energy thus obtained.

While I have described the principles of my invention in connection witha specific system, it will be understood that the system herein shownanddescribed is not to be considered as a limitation on'the scope of myinvention as set forth in the'objects thereof and in the appendedclaims.

I claim:

1. A method of eliminating from a wave modulated with substantiallyunidirectional pulses of diirerent amplitude and of appreciable durationthosepulses of greater and'lesser amplitude than a wanted pulsecomprising distorting the pulses of greater amplitude by producing sharppulse portions having high harmonic content from the leading andtrailing edges of the pulses of greater amplitude while leaving thewanted pulse substantially unchanged in form, filtering said waves toeliminate the higher'harmonics of the pulses therebyreducing'theamplitudes of the distorted pulses with respect'to theamplitude of the wanted pulse, and clipping the output pulses at a levelabove'the maximum output amplitude of the unwanted pulses.

2. A method. of eliminating from the wave modulated with pulses ofdifferent amplitude and of appreciable duration those pulses of greaterand lesser amplitude than a wanted pulse comprising applying the wave toan amplifier having an input-output characteristic in which an increasecf input potential causes the output to'increase to maximumand then todecrease toward zero, adjusting the gain of the amplifier so .that

60., When the trailing edge of.

the peak of the wanted pulse lies near the maximum of saidcharacteristic so that the wanted pulse is amplified a desired amountwithout substantial distortion and the pulses of greaterappreciablecduration from a wave modulated with pulses of difierentamplitude having pulses of greater and lesser amplitude than a wantedpulse comprising an amplifier to distort the pulses of greater amplitudethan the wanted pulse, the distortion producing sharp pulse portions ofhigh harmonic content defining the leading and trailing edges of thepulses of greater amplitude, means to filter the pulses to eliminate thehigher harmonics and thereby reduce the amplitudes of the distortedpulse with respect to the amplitude of said Wanted pulse, and means toclip the ou put pulses at a level above the maximum output amplitude ofthe unwanted pulses.

4. The system defined in claim 3 wherein the amplifier comprises a pairof tubes connected in push-pull arrangement, one of the tubes providingan input-output characteristic extending from zero to a maximum and theother of said tubes providing an input-output characteristic extendingfrom said maximum to zero.

5. The system defined in claim 3 wherein the amplifier comprises acircuit having a pair of tubes connected in push-pull arrangement and athird tube tocontrol the input potential on said tubes so as to producean input-output characteristic extending from a minimum value to amaximum value and then from said maximum value toward said minimumvalue.

6. A method of eliminating from a wave modulated with substantiallyunidirectional pulses of difierent amplitude having a predeterminedfundamental frequency content, those pulses having amplitude greater orlesser than a predetermined level, comprising distorting pulses above agiven amplitude thereby producing sharp pulse portions and relativelyincreasing the harmonic content in varying degree, from the leading andtrailing edges of the pulses above the given amplitude, filtering saidwaves to eliminate the higher harmonics of the pulses thereby reducingthe amplitude of the distorted pulses substantially proportionally totheir harmonic content, and clipping the output pulses at a level abovethat of the greater amplitude pulse after reduction.

NORMAN H. YOUNG, JR.

